(1) Technical Field
This invention is concerned with reducing scratches on substrates during chemical mechanical polishing, and more particularly to cleaning of splattered slurry from a slurry dispensing apparatus in order to prevent collection and drying of splatter from flaking off and landing on the polishing pad.
(2) Description of the Prior Art
The fabrication of integrated circuits on a semiconductor substrate involves a number of steps where patterns are transferred from photolithographic photomasks onto the substrate. Integrated circuits are typically formed on the substrates by the sequential deposition of conductive, semiconductive, or insulative layers. Selective etching of the layers assisted by photolithography forms specific structures and devices. Precise focusing for high-resolution photolithographic exposure yields well defined and highly integrated circuit structures.
During the forming of these well-defined integrated circuit structures, it has become increasingly important to construct line widths measuring in the submicron and nanomicron ranges. The photolithographic processing steps opens selected areas to be exposed on the substrate for subsequent processes such as oxidation, etching, metal deposition, and the like, providing continuing miniaturization of circuit structures. Each of the metal layers is typically separated from another metal layer by an insulation layer, such as an oxide layer. Therefore, there is a need to polish the substrate""s constructed surface to provide a planar reference. Planarization effectively polishes away non-planar entities. To enhance the quality of an overlying layer, one without discontinuities of other blemishes, it is imperative to provide an underlying surface for the structured layer that is free of scratches and is ideally planar.
Conventionally, during the fabrication of integrated circuit structures, planarizing of the overlying structured layer is accomplished by CMP. The uniform removal of material from the patterned and non-patterned substrates is critical to substrate process yield. Generally, the substrate to be polished is mounted on a tooling head which holds the substrate using a combination of vacuum suction or other means to contact the rear side of the substrate and a retaining lip or ring around the edge of the substrate to keep the substrate centered on the tooling head. The front side of the substrate, the side to be polished, is then contacted with an abrasive material such as a polishing pad or abrasive strip. The polishing pad or strip may have free abrasive fluid sprayed on it, abrasive particles affixed to it, or may have abrasive particles sprinkled on it.
The ideal substrate polishing method used by most semiconductor foundries is CMP. This choice is based on numerous factors which include; control of relative velocity between a rotating substrate and a rotating polishing pad, the applied pressure between substrate and polishing pad, choosing the polishing pad roughness and elasticity, and a uniform dispersion of abrasive particles in a chemical solution (slurry). In summary, the CMP process should provide a constant cutting velocity over the entire substrate surface, sufficient pad elasticity, and a controlled supply of clump-free polishing slurry.
A CMP tool of the prior art, shown in simplified form in FIG. 1, illustrates a substrate 38 held by a tooling head 46 which rotates about the central axis of the substrate. A circular polishing pad 40 is rotated while in contact with the bottom surface of the rotating substrate being held by the tooling head. The rotating substrate contacts the larger rotating polishing pad in an area away from the center of the polishing pad 40. A slurry arm 15 positioned above the surface of the polishing pad dispenses a slurry 17, including an abrasive and at least one chemically-reactive agent, on the polishing pad 40 by way of a supply circuit 16, and carried to the interface between the polishing pad 40 and substrate 38. A problem with prior CMP systems is that splattering of slurry on the upper and side surfaces of the splash-board 18, of the slurry arm assembly 19, occurs because of the rotational interaction between the substrate and polishing pad during the polishing operation. The spatter lands on the slurry arm, thereafter, coating the upper and side surfaces of the splashboard 18. However, between polishing operations, or during extended periods following maintenance, the slurry splatter on the slurry arm will dry to form randomly dispersed globules that consist of dried abrasive particulates on the surfaces of the splashboard. These globules may fall off the slurry arm onto the polishing pad causing scratches on the polished surface of the substrate.
In view of the above problem, there is a need to improve the cleaning of the slurry arm assembly.
A major aspect of the invention is directed to cleaning an arm assembly that is used for supplying polishing slurry to a polishing pad in a chemical mechanical polishing tool. The invention is concerned with preventing scratches on surfaces of semiconductor substrates. During the polishing operation, an aggregate of dried slurry splatter dropping off the arm assembly to the rotating polishing pad, subsequently finding its way under a rotating substrate, and damaging its polished surface.
The apparatus has an arm assembly with a self-flushing profile that is positioned over a polishing pad and at least one nozzle placed under the arm assembly for dispensing slurry against the polishing pad. A second nozzle for dispensing a cleaning liquid is positioned on top of the arm assembly to flush away slurry splatter from the top and side surfaces of the arm assembly while assisting in cleaning the polishing pad. the top surface.
Applications of the invention may include using a cleaning liquid such as deionized water. It is therefore a primary object of the present invention to provide a slurry arm assembly with a self-flushing profile for flushing slurry splatter from the top and side surfaces of the slurry arm. The slurry arm has a top view profile similar to that of the prior art.
It is another object of the present invention to trim down the surface area of the arm assembly thereby reducing area for the splatter to adhere and shaping the arm assembly to eliminate all recessed regions and sharp comers.
It is still another object of the invention to provide a spray nozzle with a multiplicity of needle size orifices mounted to the top surface of the slurry arm to direct cleaning liquid with sufficient flow volume and velocity to cover and clean the top and side surfaces of the arm assembly.
It is yet another object of the present invention to provide a cleaning nozzle, that not only cleans the major surfaces of the arm assembly but is also used to supply deionized water for water polishing the substrate after planarizing.
The present invention is a self-cleaning apparatus for use in a chemical mechanical polishing tool. The apparatus includes a slurry-dispensing arm with a first end suspended over a polishing pad, and a second end for mounting to the chemical mechanical polishing tool. A slurry-dispensing nozzle is positioned under the first end for dispensing polishing slurry against the polishing pad. The first end has a compound slanted top surface, a front face and adjoining side surfaces. The compound slanted top surface forms a longitudinal peak slanting from center to both sides and from the back end to the front face. The top surface of the first end has a liquid distribution manifold that is mounted distally from the front face and has a plurality of nozzles frontally distributed to spray deionized water to wash away slurry splatter from surfaces of the first end of the slurry dispensing arm during the water polishing cycle.
These and further constructional and operational characteristics of the invention will be more evident from the detailed description given hereafter with reference to the figures of the accompanying drawings which illustrate preferred embodiments and alternatives by way of non-limiting examples.